Let's separate those two things.

(1) coupons.com printer add-on (Install Page)

What error do you get when trying to install this add-on?

If it installs without an error but doesn't work in Firefox, check to see whether it is disabled here:

orange Firefox button (or Tools menu) > Add-ons > Plugins category
orange Firefox button (or Tools menu) > Add-ons > Extensions category

Note: Disabled add-ons cluster toward the bottom of the list on a gray background.

(2) Crashes

This article has general suggestions and also tips on how best to post information with crash details: Troubleshoot Firefox crashes (closing or quitting unexpectedly).

Start Firefox in Safe Mode to check if one of the extensions (Firefox/Tools > Add-ons > Extensions) or if hardware acceleration is causing the problem (switch to the DEFAULT theme: Firefox/Tools > Add-ons > Appearance).

• Do NOT click the Reset button on the Safe Mode start window or otherwise make changes.

• https://support.mozilla.org/kb/Safe+Mode
• https://support.mozilla.org/kb/Troubleshooting+extensions+and+themes
• https://support.mozilla.org/kb/Troubleshooting+plugins

that is not my question, I fixed that problem. My Question is, Why does firefox keep crashing when I go from websites, emails, It crashes constantly. Why

Hi liljoe48, please see the part of this article about copying your crash IDs and pasting them into a reply here: Troubleshoot Firefox crashes (closing or quitting unexpectedly).

liljoe48, the title of your original question was: "Why won't firefox let me install coupons.com printer"

Do you have a new and/or separate question from what you posted originally?

everything is running good now